There has been a proliferation of small portable electronic devices in recent years, most of which include onboard and/or detachable rechargeable batteries. Examples include laptop computers, mobile telephones, personal digital assistants, portable digital cameras, global positioning systems, and hand-held radios. The rechargeable batteries are most commonly lithium ion batteries, although other varieties are available. The small portable electronic devices typically include a removable power cord with a standard two-prong or three-prong plug, or a universal serial bus (USB) plug, for plugging into a corresponding plug receiver, which allows for recharging the onboard batteries. Also commonly available are removable power cords with a standard cigarette lighter plug, for recharging the rechargeable batteries using a cigarette lighter plug receiver in an automobile or other vehicle. Also commonly available are multi-bay chargers for multiple electronic devices and/or their detachable batteries with standard two-prong or three-prong power cords. In general these devices typically require less than 1 kW of recharging power whether from AC or DC sources.
For field operation by consumers of portable appliances such as televisions and radios, and small portable electronic devices and recharging of the batteries therein, small portable gasoline-only inverter generators have come into common use. The advantage of using small portable gasoline-only inverter generators is the much lower sound profile, lighter weight, and greater efficiency for generating the small amount of electricity needed to recharge batteries, over the period of time necessary for recharging. Gasoline or petrol for the generator is readily available at retail gasoline refueling stations.
Remote field operations, such as those in areas far away from highways, retail outlets, and the electrical grid, require participants to carry all supplies, especially consumable supplies, which will be needed to complete the operations. Not only is the total amount of supplies often minimized to reduce cost and weight, but the variety of supplies is also minimized, to reduce logistical costs and complexity in transporting materials to, and resupplying, a base camp.
To get to remote field locations, off-road and military tactical vehicles often utilize diesel-type heavy fuels, rather than gasoline or petrol. The supplies carried to such remote field locations typically only include heavy fuel, not gasoline, for the vehicles as is common in the US military with it's one fuel forward policy with a diesel type fuel (JP-8). In these cases, recharging of batteries or batteries within electronic devices is typically carried out using power generated by the vehicle, via idling the vehicle main engine while recharging the batteries or from a large 2-10 kW heavy fuel generators towed or delivered on-site by the vehicle or air support. Furthermore, in these remote and austere field locations, the noise generated by the vehicles idling engine or heavy fuel generator can be especially undesirable and often exceeding 70 dB, considering the extended period of time needed for recharging batteries or devices. Under these circumstances, the use of heavy fuels and a heavy fuel generator or idling vehicle engine is particularly inefficient for recharging small format batteries, due to the poor match between the power generated and the power required and consumed.
Generators for producing electricity are well known and have been commercially available for many years. These devices typically include an internal combustion engine. They are adapted to provide alternating current (AC) electricity, through a standard two-prong or three-prong plug receiver, at 120 or 240 volts, and at 50 to 60 Hz; also common is an additional 12 volt DC power port for charging lead acid batteries. Devices which use either gasoline-only or heavy fuels only, such as JP-8, diesel fuel, jet fuel or kerosene, are available.
Gasoline and heavy fuel engines are products of distinct and divergent technologies. Gasoline has a low-flashpoint (less than −20° C.) and high autoignition temperature (greater than 200° C.). In operation gasoline requires the proper air to fuel ratio and a spark to induce and maintain ignition. A throttle and/or fuel injector is used to meter the fuel/air mixture which is sucked into the cylinders of the engine during operation. The low flashpoint and volatility of gasoline allows starting of the spark ignition engine at temperatures below freezing, allowing for operation over a broad range of temperatures typically between −20° C. to 55° C. In order to obtain acceptable efficiency, a compression ratio of 8:1 to 12:1 is desirable for a gasoline-only engine, which is low enough to allow for manual pull-starting of the engine and the construction of simple lightweight portable engine devices made of aluminum. Improving the combustion efficiency of a gasoline engine by increasing the compression ratio further can result in autoignition (“knocking”) problems which interfere with operation and durability of the aluminum engine.
Diesel fuel and kerosene (heavy fuels) have both high flashpoints (greater than 35° C.) and low autoignition temperatures (below 200° C.). A diesel engine relies on compression induced autoignition to ignite the air/fuel mixture. Although a compression ratio of 18:1 or 20:1 is necessary to start and sustain reliable compression ignition, the superior combustion efficiency provides cost and power advantages. Furthermore, the high compression ratio requires that the fuel is sprayed into the cylinders with a pump at 70 to 80 psi, atomizing the fuel to form the liquid fuel/air mixture. The compression ignition engine cannot typically be started at low to moderate temperatures without the input of some form of high pressure from a fuel pump or thermal energy from glow plugs or block heaters. The high compression ratio requires stronger engine block materials and a heavy duty battery to start the engine, making small portable devices unrealistic.
Diesel fuel and kerosene cannot be used directly in a gasoline-only engine using a spark ignition. At ambient temperatures a gasoline-only engine would not start if heavy fuels are used. If somehow the engine were started, incomplete combustion of the heavy fuel quickly floods the engine and fouls the lubricant and spark plug. Unwanted autoignition (“knocking”) is also observed.
There exists vehicles that can be operated on both gasoline and diesel fuel. An example is the “duce-and-a-half” or M35 cargo truck. In this hypercycle, multi-fuel engine, a very high compression ratio is used: the very high compression ratio allows for efficient autoignition of both gasoline and diesel fuel. The very high compression ratio requires strong engine block materials and a large engine and for the user to add oil to the gasoline in order to maintain lubrication. Accordingly, this approach cannot be used to create a portable generator.